1. Field of the Invention
The present invention relates to improved hardware for and method of cleaning a tube bundle heat exchanger, such as a steam generator for a nuclear power plant, a boiler, or a condenser. In the embodiment of a tube bundle heat exchanger, which is a steam generator for a nuclear power plant, the method and apparatus are concerned with the removal of sediment or "sludge", which accumulates in the bottom of a heat exchanger vessel, through utilization of a repetitive blast of water directed across the bottom of the heat exchanger. The water blast is generated by a pressurized gas driven water cannon mounted to a hand hole or manway penetration in the heat exchanger shell. The water blasts tend to loosen, suspend and move the sludge so that it may be removed from the heat exchanger by water recirculation and filtering.
2. Description of the Prior Art
One of the major components in a power generating facility such as a nuclear power plant is the steam generator or heat exchanger portion of the facility. Large scale heat exchanger systems are essentially comprised of a primary system which contains a large number of individual tubes which have fluid circulation through them and a secondary system which consists of a second fluid surrounding said tubes contained within a housing which enwraps both systems. Heat is transferred from the primary fluid running through these heat exchanger tubes to the fluid in the secondary system which is itself eventually turned to steam. The steam, in turn, generates power.
These heat exchangers or steam generators have experienced many problems due to the buildup of products of corrosion, oxidation, sedimentation and comparable chemical reactions within the heat exchanger. The problem of magnetite buildup at the junctions of the primary heat exchanger tubes and the support plates for those tubes, and on the tube sheet at the bottom of the heat exchanger was treated in U.S. Pat. No. 4,320,528. This patent addresses the use of ultrasonic methods to facilitate the removal of the magnetite from those junctions.
At the bottom of the heat exchanger vessel is a tube sheet. The tube sheet is a thick metal plate that supports the numerous heat exchanger tubes, all of which completely penetrate and are sealed by the tube sheet. In addition to the problems of magnetite buildup at the junctions and inside the crevices of the primary heat exchanger tubes and their support plates, a second problem has also troubled heat exchangers such as steam generators for many years. There is a buildup of sedimentation or "sludge" which accumulates in the bottom of heat exchanger vessels. This sludge includes copper oxides, magnetite, and products of corrosion, oxidation, sedimentation and comparable chemical reactions which have not adhered to the tubing or other surfaces and therefore accumulate at the bottom. The sludge pile rests on top of the tube sheet and on top of the higher elevation support plates and may form a thick layer which may become hard and adhere to the structures. The sludge further accumulates in the crevices between the tube sheet and the primary heat exchanger tubes, which are embedded in the tube sheet, and also accumulates on the tube support plates. The problem of removing the sludge which enters the deep crevices in the tube sheet was addressed in presently pending U.S. patent application Ser. No. 370,826 filed on 4/22/82. U.S. patent application Ser. No. 370,826 solves the problem of removing sludge from the deep crevices through use of specialized ultrasonic waves which are directed in a certain way to produce the desired result.
In addition to the above two prior art references, the following prior art patents address the problem of cleaning a nuclear steam generator or else keeping it clean before it becomes occluded directly through the use of ultrasonics:
1. U.S. Pat. No. 2,664,274 issued to Worn et al. PA0 2. U.S. Pat. No. 2,987,086 issued to Branson. PA0 3. U.S. Pat. No. 3,033,710 issued to Hightower et al. PA0 4. U.S. Pat. No. 3,240,063 issued to Sasski et al. PA0 5. U.S. Pat. No. 3,295,596 issued to Ostrofsky et al. PA0 6. U.S. Pat. No. 3,433,669 issued to Kouril. PA0 7. U.S. Pat. No. 3,428,811 issued to Harriman et al. PA0 8. U.S. Pat. No. 3,447,965 issued to Teumax et al. PA0 9. U.S. Pat. No. 3,854,996 issued to Frost et al. PA0 10. U.S. Pat. No. 4,120,699 issued to Kennedy et al. PA0 11. U.S. Pat. No. 4,167,424 issued to Jubenville et al. PA0 1. Chemical Cleaning of BWR and Steam Water system at Dresden Nuc. Pw. Station, Obrecht et al., pp 1-18, (10/26/60) 21st Ann. Conf. of Eng. PA0 2. Special Tech. Pub. 42 (1962) ATSM Role of Cavitation in Sonic Energy Cleaning, by Bulat. PA0 3. R & D Status Report Nuclear Power Division, which appeared on pages 52 through 54 of the April 1981 issue of the EPRI Journal. The Article was by John J. Taylor.
All of the above referenced patents have been extensively discussed in both U.S. Pat. No. 4,320,528 or else in presently pending U.S. patent application Ser. No. 370,826 filed on 4/22/82. The following three prior art publications have also been discussed in these references:
All of the prior art discussed above employs the use of ultrasonics. While the methods discussed in the prior art, especially those in U.S. Pat. No. 4,320,528 and application Ser. No. 370,826, are very effective and valuable, the requirement of using ultrasonics has several significant disadvantages. First, expensive transducers must be used to generate the ultrasonic waves. This requires considerable effort and expense to bring the ultrasonic transducers to the site of the steam generator and then putting them in their proper place at the location of the steam generator.
A second problem which arises with prior art applications is the use of corrosive chemicals to assist in the cleaning operation. While the chemicals remove the sludge, they also eat away at the various components of the steam generator. Therefore, it is desirable to fine a method of cleaning which does not require the use of corrosive chemicals.
A second method known in the prior art for removing tube sheet sludge is called water lancing. This is in effect the use of a small steady high pressure jet of water which is shot into the sludge pile to dislodge the sludge. The method of this technique is very similar to the common user-operated car wash, having a wand with a nozzle for spraying a stream of water at the location to be cleaned. There are some problems with the water lancing process. The water lance has proven fairly effective for cutting through hard sludge but not very effective for removing the loosened sludge from the interior of the tube bundle. The inability of the water lance to remove sludge stems from the fact that the water lance jet is small, typically one tenth (1/10th) to one-hundred (1/100th) of an inch in diameter and the flow rates are small, typically ten (10) to one hundred (100) gallons per minute. In addition, the material loosened moves to the side of the water jet rather than being swept along with it. In addition, it is difficult for a small water jet to penetrate to the interior of the tube bundle. Also, the high pressure jet of water may damage the tubes. The heat exchanger must be completely drained for water lancing to be effective. The small steady high pressure jet of water may cause sludge particles to fly off and then onto the heat exchanger tubes, thereby possibly resulting in damage to these tubes.
The present invention provides a means of achieving a very large diameter and high flow rate blast of water to clean the tube sheet. In addition, the present invention may be used with the heat exchanger partially filled with water.
Water lancing is addressed in greater detail in U.S. Pat. No. 4,407,236 issued to Schukei and U.S. Pat. No. 4,492,186 issued to Helm.
A third method of cleaning heat exchangers is pressure pulse cleaning of tube bundle heat exchangers. Three presently pending patent applications by inventors Scharton and Taylor relating to different aspects and methods of pressure pulse cleaning are as follows:
1. Application Ser. No. 742,134 entitled "Method Of Pressure Pulse Cleaning A Tube Bundle Heat Exchanger". PA1 2. Application Ser. No. 604,048 entitled "Method Of Pressure Pulse Cleaning The Interior Of Heat Exchanger Tubes Located Within A Pressure Vessel Such As A Tube Bundle Heat Exchanger, Boiler, Condenser Or The Like". PA1 3. Application Ser. No. 686,242 entitled "Method Of Pressure Pulse Cleaning Heat Exchanger Tubes, Upper Tube Support Plates, And Other Areas In A Nuclear Steam Generator And Other Tube Bundle Heat Exchangers." PA1 1. An extension member can be added to the nozzle to cause the output end to come down adjacent the pile of sludge for more action against the pile of sludge. PA1 2. The barrel of the water cannon may include one or more deflector members to direct gas exiting the valve ports of the pressurized gas valve assembly down the barrel and toward the water in the barrel waiting to be impacted. PA1 3. The nozzle may further incorporate swirl vanes, which cause the water to swirl as it is shot out of the barrel. PA1 4. The top of the nozzle may contain at least one vent hole to assist in removing the expended gas from the barrel before the nest firing. PA1 5. The nozzle may include articulation means to more accurately direct the flow of water being fired out of the water cannon. PA1 6. The barrel wall may contain mixing vanes to cause the fired gas to mix more efficiently with the water it impacts and prevent the gas from hugging the side wall of the barrel and exiting directly out the nozzle. PA1 7. The barrel may include a plenum for storing greater quantities of gas before the water cannon is fired, thereby increasing the impact of the pressure on the water in the barrel. PA1 1. Recirculation System. Water can be recirculated into the heat exchanger through the water cannon nozzle and out of the heat exchanger through a suction nozzle located in the same hand-hole as the water cannon, another hand-hole, or another secondary side access port. A pump circulates the water through a filtering system where the sludge and other depris are removed from the water before it is recirculated back through the water cannon. PA1 2. Open Loop System. A source of fresh water from a water tap can be used to fill the barrel with water after each firing and a vacuuming system or draining of the heat exchanger can be used to remove the dirty water and entrained sludge from the heat exchanger. PA1 3. Gravity Fill System. The water cannon can be refilled with water from the heat exchanger after each firing if the water level in the heat exchanger is higher than the muzzle of the water cannon and the muzzle is higher than the breach of the water cannon.
These three pending applications are mentioned to provide background into the state of the art. They are not incorporated by reference.
The pressure pulser works by blasting a volume of pressurized gas into a heat exchanger partially filled with water. The blast is introduced either through a hand hole or directly from a fast opening valve immersed in the generator. The expanding gas bubble rapidly displaces the water and the shock wave from the gas blast plus the rapid water motion provides the cleaning effect.
While pressure pulse cleaning is a field-proven technique for cleaning heat exchanger support plates, it has not yet been successful for cleaning tube sheets because the pulse is non-directional. The present invention provides a means of efficiently converting the energy of the pressurized gas into water motion and of directing the water motion toward and across the heat exchanger tube sheet.
Therefore, although the use of ultrasonics combined with chemicals, the use of a jet of water, and the use of pressure pulses are all known in the prior art for cleaning and removing sludge at the bottom of a heat exchanger or steam generator, none of these methods can be employed without the significant problems discussed above. At present, there has been no prior art method for effectively removing the tube sheet sludge through a very quick, inexpensive method which does not require the use of chemicals.